Nonblocking IO Module

perlknight has asked for the wisdom of the Perl Monks concerning the following question:

I need help with an example in "Network Programming With Perl" by Lincoln Stein. Here's a snipet of the code for the IO::SessionSet Module:

package IO::SessionSet

use strict;
use Carp;
use IO::Handle;
use IO::SessionData;

use vars '$DEGUG';
$DEBUG = 0;

sub new {
   my $pack = shift;
   my $listen = shift;
   sub new {
      my $self = bless {
                         sessions => {},
                         readers  => IO::Select->new(),
                         writers  => IO::Select->new(),
                       }, $pack;
      if (defined($listen) and $listen->can('accept') {
          $self->{listen_socket} = $listen;
          $self->{readers}->add($listen);
      }
      return $self;
}
[download]

I can't find anything in this example which has $listen->can('accept'), where is he pulling this method from? Thanks.

Comment on Nonblocking IO Module Download Code

Replies are listed 'Best First'.
Re: Nonblocking IO Module by theorbtwo (Prior) on Jul 16, 2002 at 19:36 UTC
can is a method of UNIVERSAL, which means it can be called on any object. (All objects implicitly inherit from UNIVERSAL, even if they don't have any @ISA whatsoever.) It checks to see if there is an `accept()` method that could be called on `$listen`. Confession: It does an Immortal Body good.	[reply] [d/l] [select]
Re: Nonblocking IO Module by Rex(Wrecks) (Curate) on Jul 16, 2002 at 19:46 UTC
$listen is an option, an arg you can pass the new() method. It is supposed to be a listen socket. From the book description of that API: "$set = IO::SessionSet->new([$listen]) Creates a new IO::SessionSet. If a listen socket is provided in $listen, then the module automatically accepts incoming connections" Basically `$set = IO::SessionSet->new() ;` [download] is the same as doing `$set = IO::SessionSet->new() ; $set->add($listen);` [download] Does that make sense to you? Good, then what he is doing is calling the UNIVERSAL (as described above) to make sure that, if $listen exists, its a listening socket (although it can be other things too, see code on page 393 of the book) and if it is he calls his ->add method for you. *Update:* Sorry, I misread the question and just got to it in a more roundabout way :) "Nothing is sure but death and taxes" I say combine the two and its death to all taxes!	[reply] [d/l] [select]


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